C-13 NMR CHEMICAL-SHIFT OF BETA-ALKOXYVINYLKETONES .2. EMPIRICAL SUBSTITUENT EFFECTS IN BETA-ARYL-BETA-METHOXYVINYLTRIHALOMETHYLKETONE

Evaluation by empirically derived equations for. the substituent effec t (alpha, beta, gamma, delta) on the C-13 NMR chemical shifts for C-1, C-2, C-3 and C-4 in beta-aryl-beta-methoxyvinylhalomethylketones 1a-g to 2a-g [R(3)C(O)-CH=C(Ar)-OMe, where R(3) = CCl3, CF3 and Ar = p-YC6 H4 (Y = H, Me, MeO, F, Cl, Br, NO2)], taking as reference the beta-eth oxyvinyltrichloromethylketone (3), is reported. From the calculated va lues for the alpha, beta, gamma, delta, effects for each substituent i t was possible to estimate the chemical shift of each carbon of the co mpounds 1,2. The C-13 chemical shifts of the C-1, C-2, C-3, C-4 of the se compounds, can be estimated with good to rasoable precision: 84% of the calculated chemical shifts are found to be within +/-1.0ppm, and 100% are found to be within +/-1.5ppm. The Y-Effects on C-3 and C-4 ar e compared with carbon charge densities (qr).